First things first.†
When trouble shooing any electronic device, the first thing you check is
power.† All Advanced Computer Controls
equipment has 2 grounds, one analog, one digital.† BOTH MUST BE TIED BACK INDIVIDUALLY TO THE POWER SUPPLY.† This is a ďNoise ThingĒ and helps prevent
the digital noise from the processor from getting into the audio circuits.† Make sure both pins are grounded!†

IMPORTANT, always be careful when probing on a
circuit board with the power on. One slip can ruin the entire board.† It is best to have help, one person to find
the test point and hold the probes steady, the other to read the meter, record
the reading and find the next test point on the diagram.

+12 volts Ė Should appear on CR1, cathode.† That is the side toward the edge of the
board.

+5 volts Ė There are 2 five volt regulators on board.† Both have their own heat sink.† They are 3 legged devices.† The leg closest to the center of the board
is the 5 volt output.

-4.5 volts -† Can be
checked at U83 pin 1.

The next thing to check will be the audio levels into the
board.† TP1, 2, & 3 should be set
with a voltmeter to 2.7 volts AC.† Have
your helper hold a touch-tone digit while you adjust the levels on each
channel.† Remember, you have to go from
repeater to repeater or to the phone line to send the test tones depending on
where the DVR is connected.

This next test is very important, it is the touch-tone
decoder test.† If the touch-tone decoder
doesnít decode, then itís all over, nothing will work.† If your DVR had the adapter boards plugged
into the main board, set your voltmeter to DC, 5 volt range, and watch pin 15
of the chip on the adapter board. (U84 for Ch 1, U67 for Ch 2, and U72 for Ch
3)† If your board does not have the
adapter board, then watch the SSI202 IC pin 14.† See above for IC and channel numbers.† Have your helper hit touch-tone digits rapidly on the
repeater.† Watch the IC pin go high (5
volts) and low as the tones are sent.†
Fine-tune the audio level so that the touch-tone decoder decodes the
tone quickly and reliably.† If you have
a problem with this, you could have a problem with ďTwistĒ.† Check ALL digits on the touch-tone pad.† Bad twist will cause some digits to decode
reliably and others not.† To fix twist,
you will need to pick the audio from a different point in your receiver.† Bad twist is caused by some tones being louder
than others that make up a touch-tone digit. This causes the decoder to miss
the digit.

Next, we need to verify that the repeater COR signal is
working properly.† Without COR, the DVR
does not know when to start and stop recording.† With your voltmeter on DC, 25 volt range, Watch U6 pin 2 for
channel 1.† (U6-8 for Ch 2 and U7-3 for
Ch 3)† Have your helper key the repeater
and watch the voltmeter.† The meter
should follow the your helpers signal into the repeater.† If the signal goes high during the test
signal and low when there is no signal, make sure DVR Dip Switch 2 position 1
is on.† If the signal works the other
way, low when your helper is keying his radio and high when not, then turn Dip
Switch 2 position 1 off.

So far we have checked the power into the DVR and itís on
board power supplies.† We have verified
that audio is getting to the DVR and set its level.† We have also checked to see if the touch-tone decoder is working
and if twist is a factor.† At this
point, you should be able to record a signal into the DVR and have it record
it.† I like to hook a Radio Shack audio
amplifier to the DVR and listen for the test signal.† Page 257 of the 2002 Radio Shack Catalog shows it for
$11.99.† It is part number 277-1008.† You will also need something like 42-2421
1/8 mini jack to stripped wire and some clips or probes to make a nice
tester.† This amp and probes is really
useful for all kinds of repeater projects.

Hook the ground side of the audio amp to DVR ground, either
one of the grounds will be OK for this test.†
You can clip it to the bolt on the heat sink for the 5 volt regulators,
but not to the heat sink itself.† Hook
the positive side of the audio amp to the DVR output for the channel you are
testing.† Turn the audio amp about half
volume and set the output pot on the DVR to half volume as well.† Have your helper step away from the DVR so
you can hear and have them key up and enter 4***.† This is the default audio test code.† They should un-key after entering the code, then re-key and say
something really important like ďTEST 123456789987654321Ē† Once they un-key, you should hear the
important message in the test amp.† If
you donít hear the message, have them try again, check your connection to the
DVR output.† If you still donít hear
anything, try clipping the test audio amp to pin 2 of U81 (Ch 1) or U82 (Ch 2)
or U83 (Ch 3).† If you still donít get
anything, clip the test audio amp to TEST POINT 1 up by the pots. Listen to the
touch-tones and repeater audio there.†
The audio must sound clear and undistorted.† There should be no squelch noise once the user un-keys from the
repeater.† At this point if you still
donít hear audio on the output of the DVR with the audio amp you could have DVR
problems and will probably need to send it off for repairs.

If you now hear audio in the test amplifier you only have 2
more steps to complete the test.† We
need to verify that the DVR is holding the repeater up while it is
talking.† When your helper records a
test message, time the length of the message.†
If they record a 10 second message, the repeater should hang from the
time they un-key for 10 seconds before you hear the courtesy tone.† If you have that delay, this portion is
working, if not, take your voltmeter on DC 5 volt scale and measure on resistor
R3.† It is down by the 25 pin connector
on the corner of the board.† Measure for
channel 1 on the side away from the 25 pin connector.† It should go to 5 volts while the DVR is playing back recorded
audio and low once complete.† If you
donít see any level changes during playback, unhook the busy output from the
DVR to see if what it is connected to is loading down the signal.† The busy signal is a very weak output and
does not have the ability to drive heavy signal loads.† You may have to buffer the signal if you are
driving something heavy like a relay as a transistor is about all it can
drive.† If you disconnect the busy
output and you still donít see the level change, you may have to send the DVR
off for repairs.† Channel 2 can be
tested on R2 the side away from the 25 pin connector, Channel 3 should be
tested on R1 on the side toward the 25 pin connector.

By now you should be hearing DVR audio on the repeater. If
not make sure the audio output is turned all the way up on the DVR for the
channel you are testing.† Take your test
audio amp and listen to the signal as it enters the repeater from the DVR to
test your cables.† Make sure the input
pots on the repeater are adjusted properly to allow the DVR to be heard.† Listen with your audio amp as you connect and
disconnect the DVR audio from the repeater to see if the repeater is loading down
the audio.

Take each test a step at a time.† Donít make any assumptions; prove to your self that you believe
the reading that you see.† I canít say
enough about how important the test audio amp is in figuring out where the
problem lies.†